DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

SMPTE RP 168, Definition of
Vertical Interval Switching Point for
Synchronous Video Switching.
576i standards documents indicate
a precorrection of 1 ⁄2.8,
approximately 0.36, but the
Rec. 709 transfer function is
usually used. See Gamma in video
on page 261.
to 90%) of 200±20 ns is imposed, where the midpoint
of the transition is coincident with the idealized sync.
Switching between video sources is performed in the
vertical interval, to avoid disruption of sync or picture.
Switching occurs 30±5 µs after 0 H of the first normal
line of each field. In 576i systems, switching occurs
midway through line 6. (If field 2 were dominant,
switching would occur midway through line 319.)
RGB primary components
Picture information originates with linear-light primary
red, green, and blue (RGB) tristimulus components,
represented in abstract terms in the range 0 (reference
black) to +1 (reference white). In modern standards for
576i, the colorimetric properties of the primary components
conform to EBU Tech. 3213 primaries on
page 238.
Nonlinear transfer function
From RGB tristimulus values, three nonlinear primary
components are computed according to the optoelectronic
transfer function of Rec. 709 transfer function,
described on page 263. In Equation 43.1, L denotes
a tristimulus component, and V’ 709 denotes a nonlinear
primary component (one of R’, G’, or B’):
⎧⎪
4. 5L; V'709
= ⎨ 045 .
⎩⎪ 1. 099L −0. 099; 0 ≤ L<
0. 018
0. 018 ≤ L≤1
Eq 43.1
This process is loosely called gamma correction.
The R’, G’, and B’ components should maintain timecoincidence
with each other, and with sync, within
±25 ns.
Luma (Y’)
Luma in 576i systems is computed as a weighted sum
of nonlinear R’, G’, and B’ primary components
according to the luma coefficients of Rec. 601:
601
Y'= 0.299 R'+ 0. 587 G'+ 0. 114 B'
Eq 43.2
The luma component Y’, being a weighted sum of
nonlinear R’G’B’ components, has no simple relationship
with the CIE luminance, denoted Y, or relative
524 DIGITAL VIDEO AND HDTV ALGORITHMS AND INTERFACES